The Amp Garage

A 470nF 100v electrolytic is smaller than the same cap with a film dielectric. The space available for the cap is pretty tight ("C23" in that manual). That the electrolytic is 20-25% of the cost of the film-variety is also a big bonus to the manufacturer. You mean like this one I put in? :mrgreen: ...

The voltage on those transformers is going to drop more than you would expect under load, even without the big sag resistor. It is a champ transformer. ... It is better to think of it as a "blackface Princeton transformer" because as Hammond's version of a 125P1B, it is sized for a pair of 6V6s. Ha...

So the recent thread about lowering screen voltages got me thinking ... What about using a Zener to lower the screens' supply voltage? ... Try it & see if you like it. ________________________________________________________ What is the purpose of the choke between plate & screen filter caps? - It ...

... add a filter cap across R2. ... At what values for the filter cap across the 220K? What does this cap add to the recipe? The way R1 and R4 are connected now, they create More Volts Dropped when Screen Current is high. That will be "sag" but only when you play very loudly (screen current has mom...

I'm puzzled by why Fender uses a polarized electrolytic capacitor in the reverb circuit of the Blues Junior and other "blues" series amplifiers with solid state reverb. They use a 0.47 µf 100v electrolytic. ... is there any electrical purpose for choosing an electrolytic that anyone can fathom? A 4...

... screens are fed from B+2. Using a variac to take measurements at a consistent 120 VAC, here's a more comprehensive voltage report just recorded: The 6v drop from B+1 to B+2 implies 6mA through the 1kΩ resistor. If you want the 6V6s to be sensitive & easy to drive, it is better to lower the scre...

I’m trying to resurrect an ’80s MTI-era Ampeg V5. Started by replacing all caps and any resistors that were more than 5% out of tolerance. ... with Pre-Volume set to 1 and Master Volume set to 8, I was met with either no, or very low, output ... Did the amp have a problem before you started working...

... picked up a fender super sonic 22 combo ... the reverb wasn’t working but figured I could fix it. The reverb gets splash back when I tap the tank, so I assume the “return” is working. Well I ran through the usually trouble shooting stuff: rolled the tubes with known good ones, tested the tank a...

Yup, I'm aware of the 6L6GC, and one of its design features and improvements over the 6L6GB and earlier versions was ... You're missing a very basic fact: for all pentode & beam power tubes, Plate Voltage is lower than Screen Voltage half the time. Unless we never apply a signal. Question about the...

... G2 voltage ... definitely below the plate voltage. That last bit is important. ... The screen grid functions as a "virtual anode", and the plate current through the load becomes largely independent of the plate voltage ... The common catastrophic failure in power tubes is melting the screen gri...

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In the process of tweaking an old amp with single volume and tone control ... Why not use the guitar volume instead to control preamp distortion and, instead have an interstage control between the preamp and inverter? The Ampeg M-15 you're talking about didn't have any "preamp distortion." The powe...

Question - At full volume isn't C7 completely bypassed? As per suggestion by B. Ingram, I changed the filter cap, C7 from 2000pf to around 600pf. Significant change in adding more sparkle but only with volume turned down half-way. Seems the volume control essentially shorts out that capacitor when ...

… one thing that concerns me is the long lead that runs from the 10nF cap going into the PI, to the first grid of the PI. It’s kind of a weird set up, having the mixing resistors and 10nF cap stationed in between each preamp channel ... 6G3 Deluxe AA763 Deluxe Both of your donor-amps use 220kΩ resi...

... I'm not really sure it's possible to keep the operating points anywhere similar with the 6AV6 as a CF. A cathode follower is an excellent place for you to use a JFET instead of a tube. The cathode-follower has 100% negative feedback, so the tube wasn't "contributing tube-y-ness" anyway. And the...